Centrifugal compressors in gas turbine engines generally include a diffuser located radially outwardly of a centrifugal impeller such as to receive the airflow coining therefrom. In applications where the gas turbine engine ingests hard particles such as sand with aluminium oxide and silicon oxide content, for example in helicopter turboshaft engines that ingest significant amounts of sand and dust during take-off and close-to-ground flights, such hard particles are usually mixed in the compressor air and can travel at an ultrasound velocity when entering the diffuser. These high speed abrasive particles can cause erosion of bores defined through the diffuser and directing the airflow, thus increasing the diameter of these bores, which usually causes a loss of compressor efficiency and of surge margin and can even cause surging if the surge margin is exceeded.
However, diffuser bore surfaces are relatively hard of access and generally define sharp edges, and as such are difficult to treat to improve their erosion resistance.
Accordingly, improvements are desirable.